POROSITY CONTROLLED PHOTOELECTRICAL PROPERTIES OF GaP

Photoelectrical properties of bulk and porous GaP were investigated in a temperature interval 10 - 300 K. It was found that the porosity increases the photosensitivity of the material. The photoelectrical properties of nanoporous GaP are explained on the basis of a porosity controlled potential barrier pattern. New possibilities for the elaboration of porous material based optoelectronic devices are probed. Porous GaP layers were obtained by anodic etching of n-type Te-doped GaP crystals with electron concentration n = 1 10 18 cm -3 in an electrochemical cell with a Pt-working electrode using a 0.5 M aqueous solution of H2SO4. A 5 MeV Kr + ion preimplantation was used for the control of the layer morphology and porosity degree. The etching process was carried out both in darkness and with the in-situ illumination for different duration with various current densities. The formation of porous structures was proved by scanning electron microscope. As a result of dissolution porous structures with different average pore and skeleton thickness were formed depending on the technological conditions of electrochemical processing. Coplanar ohmic Ni-AuGe-Ni contacts were evaporated on samples subjected to subsequent rapid thermal annealing. White light from a Narva halogen lamp passed through a MDR-2 monochromator as well as an Ar + laser beam was used for the photoconductivity (PC) excitation. Neutral density filters were used to reduce the intensity of the light at the sample. The samples were included in a circuit with a DC source and an electrometer for PC measurements. Since the PC decay time is long enough, a mechanical shutter was used in the PC relaxation experiments. The signal from the electrometer was introduced in an IBM computer via IEEE-488 interface for further data processing. The experiments were performed in a temperature interval 10 - 300 K, the samples being mounted in LTS-22-C-330 Workhorse-type optical cryogenic system.